Okla. Stat. tit. 10 § 7507-1.1
An adult person may be adopted by any other adult person, with the consent of the person to be adopted or his guardian, if the court shall approve, and with the consent of the spouse, if any, of an adoptive parent, filed in writing with the court. The provisions of Sections 9 through 36 of this act shall not apply to the adoption of a competent adult person. A petition therefor shall be filed with the district court in the county where the adoptive parents reside. After a hearing on the petition and after such investigation as the court deems advisable, if the court finds that it is to the best interests of the people involved, a decree of adoption may be entered which shall have the legal consequences stated in Section 37 of this act.
Okla. Stat. tit. 10, § 7507-1.1